APNCEIC BLOOD, EUPNCEA, AND DYSPNCEA. 663 



cessation of the artificial respiration (Hook, 1667), the blood being so arterialised 

 that it no longer stimulates the respiratory centre. If a person takes a series of 

 rapid, deep respirations his blood becomes surcharged with oxygen, and long 

 " apnoeic pauses " occur. 



Apnoeic Blood. A. Ewald found that the arterial blood of apnoeic animals was completely 

 saturated with 0, while the C0 2 was diminished ; the venous blood contained less than normal 

 this latter condition being due to the apnoeic blood causing a considerable fall of the blood- 

 pressure and consequent slowing of the blood-stream, so that the can be more completely 

 taken from the blood in the capillaries (Pfiitger). The amount of used in apnoea on the whole 

 is not increased ( 127). Gad remarks that during forced artificial respiration, the pulmonary 

 alveoli contain a very large amount of atmospheric air; hence, they are able to arterialise the 

 blood for a longer time, thus diminishing the necessity for respiration. According to Gad and 

 Knoll, the excitability of the respiratory centre is reduced during apncea, and this is caused 

 reflexly during artificial respiration by the distension of the lungs stimulating the branches of 

 the vagus. In quite young mammals apnoea cannot be produced (Runge). 



[Drugs. If the excitability of the respiratory centre be diminished by chloral, apnoea is 

 readily induced, while, if the centre be excited, as by apomorphine, it is difficult to produce it.] 



2. Eupnoea. The normal stimulation of the respiratory centre, eupnoea, is 

 caused by the blood, in which the amount of and C0 2 does not exceed the normal 

 limits ( 35 and 36). 



3. Dyspnoea. All conditions which diminish the O and increase the C0 2 in 

 the blood circulating through the medulla and respiratory centre cause acceleration 

 and deepening of the respirations, which may ultimately pass into vigorous and 

 laboured activity of all the respiratory muscles, constituting dyspnoea, when the 

 difficulty of breathing is very great ( 134). [Changes in the rhythm, 111.] 



During normal respiration, and with the commencement of the need for more air, according 

 to Gad, the gases of the blood excite only the inspiratory centre ; while the expiration follows 

 owing to reflex stimulation of the pulmonary vagus by the distension of the lungs (p. 666). He 

 is also of opinion that the normal respiratory movements are excited by the C0 2 . 



[Muscular work, as is well-known, increases the respirations and may even cause dyspnoea. 

 This is not due to the nervous connections of the muscles or other organs with the respiratory 

 centre, but to changes in the blood. Geppert and Zuntz have shown, however, that the result 

 cannot be explained by changes in the blood caused either by diminution of or increase of 

 C0 2 . It seems to be due to the blood taking up some as yet unknown products from the con- 

 tracting muscle, and carrying them to the respiratory centre, which is directly excited by them. 

 The nature of these substances is unknown. It has been shown that the alkalinity of the 

 blood is reduced by the formation of an acid. The substances, whatever they may be, are not 

 excreted by the urine, and are, therefore, perhaps readily oxidised (Loewy). C. Lehmann has 

 proved that, in rabbits, the acidification of the blood produced by muscular exertion plays an 

 important part in the stimulation of the respiratory centre.] 



4. Asphyxia. If blood, abnormal as regards the amount and quality of its 

 gases, continue to circulate in the medulla, or if the condition of the blood become 

 still more abnormal, the respiratory centre is over-stimulated, and ultimately 

 exhausted. The respirations are diminished both in number and depth, and they 

 become feeble and gasping in character; ultimately the movements of the 

 respiratory muscles cease, and the heart itself soon ceases to beat. This constitutes 

 the condition of asphyxia, and if it be continued, death from suffocation takes 

 place. (Langendorff asserts that in asphyxiated frogs the muscles and grey 

 nervous substance have an acid reaction.) If the conditions causing the abnormal 

 condition of the blood be removed, the asphyxia may be prevented under favourable 

 circumstances, especially by using artificial respiration ( 134); the respiratory 

 muscles begin to act and the heart begins to beat, so that the normal eupnceic 

 stage is reached through the condition of dyspnoea. If the venous condition of the 

 blood be produced slowly and very gradually, asphyxia may occur without there 

 being any symptoms of dyspnoea, as happens when death takes place quietly and 

 very gradually ( 324, 5). 



Causes of Dyspnoea. (1) Direct limitation of the activity of the respiratory organs ; 



diminution of the respiratory surface by inflammation, acute oedema ( 47), or collapse of the 



